Turn iMessage On/Off - Apple® iPhone® 4

[Device-Specific Instructions]

If you've recently changed OS types (Apple, Android, Windows, BlackBerry) or are unable to send/receive text messages on your iPhone or messages from other iPhones aren't blue (iMessages), this may help. Our Troubleshooting Assistant can help you with other device issues if you aren't currently using the tool.

From the Home screen, navigate: Settings > Messages.

Tap the iMessage switch to turn on (in the green or ON position) or off.

iMessage is an Apple messaging service that allows unlimited text messages between Apple devices with iOS 5 or greater.